3.7 Merc only turns 15 degrees

My father and I were recently gifted a 1987 Sting Ray SVC 190 SS. 3.7L Mercruiser (Volvo) with 2 barrel inboard/outboard. Quick history: boat has been underwater a couple times, but has been fixed and running since the last time it was submerged. The last time it was running was 3 years ago. To start, I wanted to see if the motor would turn by hand, no go. Checked oil, level good and oil clean. Coolant reservoir empty (pulled thermostat housing and found quarts of nice green antifreeze). Pulled plugs (looked good except for #1, slight green/white scale). Poured Marvel mystery oil into cylinders. Waited 1 day. Using bolts in the balancer and a pry bar, was able to turn the motor only 15 degrees, back and forth. At the end of each rotation it felt spoungy/springy. Loosened rocker arms, all valves closed, placed pushrod into cylinder bores, cylinders move. Removed belt (power steering), removed fuel pump, removed thermostat housing(pump impeller turned). Driveshaft to outdrive turns, prop turns when in gear. I am new to boats, but have been working on out of water motors for many years. What could be binding? Also, poured marvel M. O onto the lifters. Any and all help will be appreciated.

Thanks,
Brandon

Re: 3.7 Merc only turns 15 degrees

Hi Brandon,
Welcome aboard.

When you say "3.7L Mercruiser (Volvo)" - not sure what you mean by that. It sounds like you have Mercruiser - not a Volvo. They are two different things.

Also - you have an engine that is problematic at best... and it sounds like yours is not at its best.

A few quick suggestions...

- Download the appropriate manual from the adults only sticky at the top of the page.

- Take off the outdrive.

- Check the stator - it is my understanding that the magnets can come off and cause things to lock up.

- Do a search of the "Mercruiser 470" here on the board and read up on what you have.

Good luck! I think you are going to need it.

Re: 3.7 Merc only turns 15 degrees

This may call for pulling the motor and ripping it down. The fact that the engine hasnt started in three years would justify that not to mention its been submerged.

I could possably be a timing gear or the chain, or possibly a bad bearing on the crank.

Check out 3.7L rebuild link in my signiture. It may help!

Re: 3.7 Merc only turns 15 degrees

Thanks for the lightning quick responses. The motor is a Merc. 3.7L model MCM. I said volvo because it is not a GM, and I thought I found a post here that mentioned it was a Volvo...anyway. As long as I can get it turning I can get it started. I thought about the possibilities mentioned, and the only one that seems to make sense would be the timing chain. I am hoping that it is frozen, and that the spoungy feeling is the tensioner. I don't feel that it would be a bearing, that would give me a grinding feeling when turning, and it doesn't seem to have anything to do with the pistons.
The boat is currently on a lift, and I'm not sure if it will float (rubbers on the outdrive seem to be shot). Also, I don't have a trailer for it. My next step will be to take the balancer and front cover off. I'll do that later and let you know what I find. Thanks again.

Brandon

Re: 3.7 Merc only turns 15 degrees

BrandonS said:

....I said volvo because it is not a GM, and I thought I found a post here that mentioned it was a Volvo.....

Click to expand...

It is a custom block made and used only by Mercruiser. It isnt as most I/O engines that have a automotive core. It does how ever share parts with a 460 Ford such as the head.

Keep us updated.

Re: 3.7 Merc only turns 15 degrees

Take the outdrive off first,that could be siezed
download the manual, theres a lot more involved than just taking the front balalncer off and thinking you can remove the timing cover

Re: 3.7 Merc only turns 15 degrees

Is there a way to disconnect the outdrive from the motor without removing it? Driveshaft or U-joint disconnect?

Re: 3.7 Merc only turns 15 degrees

No way to do it other than remove it.

Re: 3.7 Merc only turns 15 degrees

BrandonS said:

Is there a way to disconnect the outdrive from the motor without removing it? Driveshaft or U-joint disconnect?

Click to expand...

takes 10 minutes to remove. you need to remove it anyway to replace the bellows that you said were rotted.

EDIT: rereading your post, you said driveshaft and prop turn in gear? barring a bad coupler, if your prop is turning in gear/driveshaft turning, so's your engine...

Re: 3.7 Merc only turns 15 degrees

I would have also had guessed that the outdrive was all the way up which would cause binding on the u-joints. I agree, remove the outdrive to isolate if the problem is the engine or the outdrive. Being under water a few times, was the u-joints and seals replaced for the thru hull? You may or may not have a lot of problems or big problems. It will take some isolating them to identify what it will take to make it work. You may be lucky and it is just two u-joints. You can also be looking at an engine replacement/overhaul.

Re: 3.7 Merc only turns 15 degrees

BrandonS said:

Is there a way to disconnect the outdrive from the motor without removing it? Driveshaft or U-joint disconnect?

Click to expand...

Ayuh,... It's 8 nuts, 10 minutes-Tops,+ a $6. gasket set....

My guess is, you'll be diggin' a 'ell of alot Deeper before you go for a boat ride,....

Re: 3.7 Merc only turns 15 degrees

My father was able to contact the mechanic that worked on the boat before (not sure if a history of the boat was necessary). He came down, and put more force on the crowbar that we used to turn the crank than I would have. Now it rotates!!!! Should have very little problems getting it running now. The only question now...will it float? I'll have to replace all the rubber on the outdrive, but it will be fun.
Anyone have any suggestions on how to keep muskrats from eating the rubber?

Thanks again for all the help. I'll be around to help as much as I can.

Brandon

Re: 3.7 Merc only turns 15 degrees

Anyone have any suggestions on how to keep muskrats from eating the rubber?

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Ayuh,... Keep the drive Down...
And, shoot the rats....

Re: 3.7 Merc only turns 15 degrees

BrandonS said:

He came down, and put more force on the crowbar that we used to turn the crank than I would have. Now it rotates!!!! Should have very little problems getting it running now.

Click to expand...

Not to rain on your parade.... but just because it has been "broken free" and now rotates, that doesn't necessarily mean you will have "very little problems getting it running now." There is a whole lot more to getting an engine running well than simply being able to rotate it with a crowbar. I'm not suggesting you can't get it running, but simply pointing out you have accomplished step one of about a hundred. Good luck and keep us informed of your progress!

Re: 3.7 Merc only turns 15 degrees

If it were mine I would get the engine running first.

Re: 3.7 Merc only turns 15 degrees

I may have overstated the simplicity of getting the motor started, but I am a pretty experienced mechanic, so it shouldn't be that hard.

One more question: How heavy is the outdrive unit? I would like to replace the bellows without removing the boat from the lift that it is on. Plus, even if I had a trailer, I'm not sure I'd be able to get it to the trailer without it sinking, with all the bellows missing.

Brandon

Re: 3.7 Merc only turns 15 degrees

One more question: How heavy is the outdrive unit?

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Ayuh,... 80lbs...